The present invention generally relates to the elemental analysis of deposits found on surfaces of machinery parts and components. More particularly, the present invention relates to an in situ laser plasma spectroscopy (LPS) analysis and identification of material deposits found on the surfaces of power generating equipment components such as gas turbine compressor blades.
Unknown contaminants and/or deposits may be found accumulating on the surfaces of various parts and components of power generating machines and equipment, e.g., on compressor blades of turbine engines, during the ordinary course of operation. Such deposits have a potential for inducing performance degradation and component damage. For example, in the case of a gas turbine compressor, such deposits may significantly affect the airflow and overall operating efficiency. If the composition and character of such a deposit is known, an appropriate corrective action may be taken. However, such deposits often occur on parts and components that are relatively inaccessible without substantial disassembly of the particular apparatus or equipment involved.
Using conventional analysis techniques and tools, at least a partial disassembly of an apparatus and/or removal of an affected part is often required in order to gain access to the deposit or surface contaminant for performing an analysis. In the case of large power generating equipment, such as a gas turbine compressor, the time and cost of performing even a partial disassembly can be enormous. Consequently, there is a need for a more practical and economical means for performing analysis of deposits found on component surfaces of machinery without requiring substantial disassembly of such.
Laser Plasma Spectroscopy (LPS), also known as Laser-Induced Breakdown Spectroscopy (LIBS) or Laser-Induced Plasma Spectroscopy (LIPS) (as well as by other names) is a well-understood technique for performing both qualitative and quantitative elemental analysis of materials and compounds. Such LPS techniques may be used more or less effectively for procuring elemental analysis of many different substances including compounds in the form of gases, liquids or solids. In accordance with the basic technique, the light output from a pulsed laser is focused onto the surface of an object. Assuming the focused laser pulse has sufficient intensity, a small amount of material at the surface of the object is vaporized forming a high-temperature plasma consisting of ions and excited atoms that emit a particular spectrum of light radiation which corresponds to elemental constituents of the vaporized material. The elemental composition of the irradiated material may then be accurately determined through spectral analysis of light radiation emitted from the plasma. Multiple plasma generating laser pulses are often used in succession to obtain additional spectral data to improve the accuracy of the analysis.
LPS also has certain advantages over other types of elemental analytical techniques. For example, when using an LPS technique for elemental analysis, extensive preparation of a sample to be analyzed is not required and only a small quantity of the sample material (e.g., on the order of nanograms) is vaporized during analysis. In addition, an LPS analysis may be performed fairly rapidly. A plasma adequate for producing a spectrum sufficiently luminous to enable elemental identification via spectroscopy may be obtained using only a single laser pulse. Moreover, since many different wavelengths from the plasma spectrum may be simultaneously analyzed, multiple constituent elements may be identified at the same time.
Laser plasma spectroscopy (LPS) has proven to be useful in a variety of different laboratory and industrial applications. See, for example, the following U.S. patents: U.S. Pat. No. 6,008,896 to Sabsabi et al. entitled xe2x80x9cMethod And Apparatus For Spectroscopic Analysis of Heterogeneous Materialsxe2x80x9d, issued Dec. 28, 1999; U.S. Pat. No. 5,798,832 to Hnilica et al. entitled xe2x80x9cProcess And Device For Determining Element Compositions And Concentrationsxe2x80x9d, issued Aug. 25, 1998; U.S. Pat. No. 5,751,416 to Singh et al. entitled xe2x80x9cAnalytical Method Using Laser-Induced Breakdown Spectroscopyxe2x80x9d, issued May 12, 1998; International Patent No. WO 99/45368 to Nelson et al. entitled xe2x80x9cImproved Laser Spectral Analyzer With Sample Location Detectorxe2x80x9d, published Sep. 10, 1999; U.S. Pat. No. 5,757,484 to Miles et al. entitled xe2x80x9cStandoff Laser Induced-Breakdown Spectroscopy Penetrometer Systemxe2x80x9d, issued May 26; U.S. Pat. No. 6,147,754 to Theriault et al. entitled xe2x80x9cLaser Induced Breakdown Spectroscopy Soil Contamination Probexe2x80x9d, issued Nov. 14, 2000; and U.S. Pat. No. 5,715,053 to Loge entitled xe2x80x9cMethod For Determining The Concentration of Atomic species In Gases And Solidsxe2x80x9d, issued Feb. 3, 1998. However, the conventional LPS techniques disclosed in the above mentioned patents have various drawbacks which tend to render them unsuitable for use in the identification of surface deposits found on machinery and, in particular, on components of power generating equipment and the like.
Although LPS is generally recognized as a valid technique for analyzing and identifying the elemental compositional makeup of various materials, there exists a problem in that an object being examined using LPS may suffer significant damage by continued firing of the laser. For example, surface damage incurred through ablation by the laser during an LPS process may significantly reduce the lifetime of a gas turbine compressor blade. In addition, conventional LPS systems are not readily portable and are not generally convenient to use at the location sites of power generating equipment. Many LPS systems are large and rather bulky. Also, the plasma generating laser light output of many LPS systems is not easy to direct and focus onto a particular target, especially if that target is within a relatively small or confined area or is at a location or part within a larger machine and is difficult to see and/or reach. Moreover, conventional LPS systems typically do not provide rapid analysis of LPS data and make that analysis available to a user in near real-time while at the location of the equipment or machinery being examined.
In one aspect of the present invention, a portable system and method is provided that allows in situ testing and near-real time elemental analysis and identification of deposits or other contaminants found on the surfaces of machine parts or other objects wherein minimal or no damage to the substrate material beneath the deposit is incurred as a result of the testing and analysis procedures. Elemental identification is based on a technique of laser plasma spectroscopy (LPS), to wit: a technique wherein the output of a high peak power pulsed laser is focused to a small spot on an object surface sufficient to result in the vaporization of material within the focal volume of the laser pulse and the formation of a luminous plasma which is spectrally analyzed to identify the elemental composition.
In an example embodiment of the invention, a time-resolved spectral profile of the light radiation emitted from one or more plasma events created from a surface deposit during LPS is obtained using a gated PDA (photo-diode array) or ICCD (intensified charge-coupled device) detector coupled to a portable spectrometer. The laser light used for producing the plasma is electronically shuttered (blocked) upon detection of the elemental profile of the particular substrate material belonging to the machine part or object on which a found deposit is being analyzed. The shuttering is initiated after no more than one laser pulse has hit the substrate, prior to the occurrence of any significant ablation damage to the part. Acquisition, storage and analysis of plasma spectral data acquired from the detector is accomplished in situ using a portable or hand-held computer or like device, which is also used to display a spectral intensity profile of the plasma. In addition, the portable computer device is, or may be, programmed to identify the elemental composition of the deposit through comparison analysis with known spectral profiles that are either stored within the computer or accessed, for example, via a telecom link from a remote database.
In accordance with another aspect of the present invention, analysis of the plasma spectrum may be performed at a location that is effectively xe2x80x9cremotexe2x80x9d from the site of generated plasma on a machine part or other object. A fiber-optic probe or borescope is used to transmit the light from the laser source to a location of interest, such as on a machine part, and to return plasma light radiation emissions back to a spectrometer and detector. In this regard, a further beneficial aspect of the present invention is that it facilitates diagnostic access to parts of a turbine compressor (or other machinery) that are ordinarily difficult to access, thus precluding the need for any substantial disassembly of the object or machinery under examination.
In another aspect of the present invention, the LPS system is able to resolve, both spectrally and temporally, emissions from a plasma generated primarily from only the substantive material of an examined deposit present on the surface of an examined machine component or object and without producing any significant ablation damage to the machine component or object itself.
Yet another beneficial aspect of the present invention is that it substantially reduces the possibility that the surface of an examined object or machine component might sustain damage caused by ablation from the laser during an LPS process.